Origin of Tokamak Density Limit Scalings

Gates, D.; Delgado‐Aparicio, L.

doi:10.1103/physrevlett.108.165004

Cited by 87 publications

(98 citation statements)

References 21 publications

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AbstractIn previous work [1], the onset criterion for radiation driven islands [2] in combination with a simple cylindrical model of tokamak current channel behavior was shown to be consistent with the empirical scaling of the tokamak density limit [3]. A number of the unexplained phenomena at the density limit are consistent with this novel physics mechanism.

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mentioning

confidence: 49%

“…As a result of this effort an agreed upon empirical scaling, referred to as the Greenwald limit [3], n e < I p πa 2 (1) has been developed and extensively verified against international databases. Here,n e is the line averaged (as from an interferometer) electron density, I p is the total plasma current, and a is the plasma geometric minor radius.…”

Section: Introductionmentioning

confidence: 99%

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Physics of radiation-driven islands near the tokamak density limit

Gates¹,

Delgado‐Aparicio²,

White³

2013

Nucl. Fusion

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In previous work [1], the onset criterion for radiation driven islands [2] in combination with a simple cylindrical model of tokamak current channel behavior was shown to be consistent with the empirical scaling of the tokamak density limit [3]. A number of the unexplained phenomena at the density limit are consistent with this novel physics mechanism. In this work, a more formal theoretical underpinning, consistent with cylindrical tearing mode theory, is developed for the onset criteria of these modes. The appropriate derivation of the radiation-driven addition to the modified Rutherford equation is discussed.Additionally, the ordering of the terms in the MRE is examined in a regime near the density limit. It is hoped that given the apparent success of this simple model in explaining the observed global scalings will lead to a more comprehensive analysis of the possibility that radiation driven islands are the physics mechanism responsible for the density limit.In particular, with modern diagnostic capabilities detailed measurements of current densities, electron densities and impurity concentrations at rational surfaces should be possible, enabling verification of the concepts described above.

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mentioning

confidence: 49%

Section: Introductionmentioning

confidence: 99%

Physics of radiation-driven islands near the tokamak density limit

Gates¹,

Delgado‐Aparicio²,

White³

2013

Nucl. Fusion

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“…The other η-related effect is a non-axisymmetric one: the gas cools the plasma locally and therefore suppresses the current locally, which should lead to the growth of magnetic islands with their O-point at the gas deposition location. This mechanism is involved as well in radiation driven islands, which have been invoked recently to explain density limit disruptions [9]. To a certain extent, numerical experiments allow discriminating between the three above-mentioned mechanisms.…”

Section: Physics Of the Pre-thermal Quench Phasementioning

confidence: 99%

Progress in understanding disruptions triggered by massive gas injection via 3D non-linear MHD modelling with JOREK

Nardon

Fil

Hoelzl

et al. 2016

Plasma Phys. Control. Fusion

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3D non-linear MHD simulations of a D 2 massive gas injection (MGI) triggered disruption in JET with the JOREK code provide results which are qualitatively consistent with experimental observations and shed light on the physics at play. In particular, it is observed that the gas destabilizes a large m/n = 2/1 tearing mode, with the island O-point coinciding with the gas deposition region, by enhancing the plasma resistivity via cooling. When the 2/1 island gets so large that its inner side reaches the q = 3/2 surface, a 3/2 tearing mode grows. Simulations suggest that this is due to a steepening of the current profile right inside q = 3/2. Magnetic field stochastization over a large fraction of the minor radius as well as the growth of higher n modes ensue rapidly, leading to the thermal quench (TQ). The role of the 1/1 internal kink mode is discussed. An I p spike at the TQ is obtained in the simulations but with a smaller amplitude than in the experiment. Possible reasons are discussed.

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“…A recent explanation by Gates and Delgado-Aparicio [14] suggests that the limit is due to the destabilisation of magnetic islands (in the outer regions rather than the core) by radiation losses: at high enough density these cannot be overcome by local Ohmic heating, and this leads to further island growth. As the authors themselves note, this mechanism would not operate in stellarators.…”

Section: Macroscopic Equilibrium and Stabilitymentioning

confidence: 99%

Stellarator and tokamak plasmas: a comparison

Helander

Beidler

Bird

et al. 2012

Plasma Phys. Control. Fusion

138

181

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An overview is given of physics differences between stellarators and tokamaks, including magnetohydrodynamic equilibrium, stability, fast-ion physics, plasma rotation, neoclassical and turbulent transport, and edge physics. Regarding microinstabilities, it is shown that the ordinary, collisionless trapped-electron mode is stable in large parts of parameter space in stellarators that have been designed so that the parallel adiabatic invariant decreases with radius. Also, the first global, electromagnetic, gyrokinetic stability calculations done for Wendelstein 7-X suggest that kinetic ballooning modes are more stable than in a typical tokamak.

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Origin of Tokamak Density Limit Scalings

Cited by 87 publications

References 21 publications

Physics of radiation-driven islands near the tokamak density limit

Physics of radiation-driven islands near the tokamak density limit

Progress in understanding disruptions triggered by massive gas injection via 3D non-linear MHD modelling with JOREK

Stellarator and tokamak plasmas: a comparison

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